Legacy DDS files with a DDS_HEADER size of 24

[0xC0000054]

Related to 0xC0000054/pdn-ddsfiletype-plus#16

The OP says the files are from S.T.A.L.K.E.R.: Shadow of Chernobyl, a DX 9-based game.
I have no idea why these files use 24 for the DDS_HEADER size, did they forget the 1 when typing 124.

A sample for your test suite: dds_header size 24.zip

I plan to submit a PR with the following fix. and an updated check in the DX 10 code path:

if (flags & DDS_FLAGS_PERMISSIVE)
{
    if (pHeader->size != 24 /* Known variant */
        && pHeader->size != sizeof(DDS_HEADER))
    {
        return HRESULT_E_NOT_SUPPORTED;
    }
}
else if (pHeader->size != sizeof(DDS_HEADER))
{
    return HRESULT_E_NOT_SUPPORTED;
}